In-chamber electron detector

Abstract

A secondary particle detector 302 for a charged particle beam system 300 includes a scintillator 304 and a transducer 312 , such as a photomultiplier tube, positioned within a vacuum chamber 107 . Unlike prior art Everhart-Thornley detectors, the photomultiplier is positioned within the vacuum chamber, which improves detection by eliminating optical couplings and provides flexibility in positioning the detector.

1. A charged particle beam system, comprising:
 a source of charged particles; 
 a focusing column for forming a charged particle beam from the charged particles emitted by the charged particle beam source; 
 a sample vacuum chamber containing a sample stage for holding a sample to which the charged particle beam is directed; 
 a secondary particle detector positioned off the optical axis within the vacuum chamber, the detector including: 
 a conductive grid providing an electric field for attracting secondary particles to the detector; 
 a scintillator for emitting light when impacted by a secondary electron, the scintillator positioned above a plane defined by the sample surface and 
 a photomultiplier tube for detecting the light emitted by the scintillator and converting the light to an electric current; 
 characterized in that the scintillator and photomultiplier tube are all positioned within the sample vacuum chamber. 
 
     
     
       2. The charged particle beam system of  claim 1  further comprising a second source of charged particles and a second focusing column for forming a charged particle beam from the charged particles emitted by the second charged particle beam source. 
     
     
       3. The charged particle beam system of  claim 1  in which the position of the secondary particle detector is adjustable within the vacuum chamber to improve the collection of secondary particles. 
     
     
       4. The charged particle beam system of  claim 1  in which the secondary particle detector includes an ion-to-electron converter. 
     
     
       5. The charged particle beam system of  claim 1  further comprising a light tube to conduct light from the scintillator to the photomultiplier tube. 
     
     
       6. The charged particle beam system of  claim 5  in which the light tube is less than 25 mm long. 
     
     
       7. The charged particle beam system of  claim 5  in which the light tube is less than 15 mm long. 
     
     
       8. The system of  claim 5  in which the light guide comprises a rigid rod of a transparent material positioned between the scintillator and the photomultiplier tube. 
     
     
       9. The system of  claim 5  in which the light guide comprises a solid plastic or glass rod that conducts light from the scintillator into a single photomultiplier tube. 
     
     
       10. The charged particle beam system of  claim 1  in which the secondary particle detector is less than 120 mm long. 
     
     
       11. The charged particle beam system of  claim 10  in which the secondary particle detector is less than 60 mm long. 
     
     
       12. The charged particle beam system of  claim 1  further comprising an ion-to-electron converter positioned before the scintillator. 
     
     
       13. The charged particle beam system of  claim 12  in which the ion-to-electron converter includes a cylindrical surface for converting secondary ions to electrons. 
     
     
       14. The system of  claim 1  in which the focusing column includes an objective lens and in which the conductive grid attracts secondary electrons from the sample without the secondary electrons passing through the objective lens. 
     
     
       15. The charged particle beam system of  claim 1  in which the scintillator comprises a phosphor. 
     
     
       16. The charged particle beam system of  claim 1  in which the scintillator comprises a light-emitting plastic or a garnet oxide. 
     
     
       17. The charged particle beam system of  claim 1  in which the input grid is hemispherical. 
     
     
       18. The charged particle beam system of  claim 1  in which the center of the input grid is positioned further away from the surface of the scintillator than are the edges of the input grid. 
     
     
       19. A method of detecting secondary electrons, comprising:
 directing a primary charged particle beam toward a sample surface in a sample vacuum chamber; 
 attracting by an electric field provided by a conductive grid charged particles emitted from the surface upon impact of the primary charged particle beam toward a material within the vacuum chamber that emits photons upon the impact of a charged particle, the material positioned above the sample plane; 
 detecting the photons and converting the photons to an electric current using a photomultiplier tube, the current being proportional to the number of charged particles detected from the sample surface upon impact of the charged particle beam; and 
 conducting the electric current from the vacuum chamber, 
 characterized in that the photons are converted to an electric current within the vacuum chamber. 
 
     
     
       20. The method of  claim 19  in which directing a primary charged particle beam toward a sample surface in sample vacuum chamber includes directing an ion beam or an electron beam. 
     
     
       21. The method of any of  claims 19  further comprising conducting photons through a light tube toward the photomultiplier tube. 
     
     
       22. The method of any of  claims 19  in which detecting and converting the photons to an electric current within the vacuum chamber includes detecting and converting the photons to an electric current within a device that is less than 15 cm long. 
     
     
       23. The method of any of  claims 19  in which attracting charged particles emitted from the surface upon impact of the primary charged particle beam further includes attracting ions and further comprising converting the ions to electrons. 
     
     
       24. A secondary particle detector sufficiently compact for being positioned within the vacuum chamber of a scanning electron microscope, the detector comprising:
 a scintillator for emitting light when impacted by a secondary electron; 
 a conductive grid for providing an electric field attracting secondary electrons to the scintillator; 
 a photomultiplier tube for detecting the light emitted by the scintillator and converting the light to an electric current; 
 a light guide for guiding light from the scintillator to the photomultiplier tube, the light guide providing a light path from the scintillator to the photomultiplier tube that is shorter than 50 mm, the secondary particle detector bring sufficiently compact for being positioned above the plane of the sample in a scanning electron microscope. 
 
     
     
       25. The secondary particle detector of  claim 24  in which the light guide providing a light path from the scintillator to the photomultiplier tube that is shorter than 25 mm. 
     
     
       26. The secondary particle detector of  claim 24  in which the light guide providing a light path from the scintillator to the photomultiplier tube that is shorter than 15 mm. 
     
     
       27. The secondary particle detector of  claim 24  in which scintillator, photomultiplier tube, and light guide together are less than 100 mm long.